20/08/2026
Got a hot water cylinder rather than a combi? Then this one matters, especially if yours is unvented and has never been serviced.
Quick way to tell which you have: look in the loft. A big cold water tank up there means a vented system, gravity-fed, which is why the pressure at your taps depends on how high that tank sits. No tank at all, and a cylinder covered in valves with a pipe running outside, means unvented. That one is fed straight off the cold mains, so you get strong showers without a pump and can run more than one outlet at once.
The catch with unvented is that it is a sealed pressure vessel. Water expands as it heats, so the cylinder carries an expansion vessel, a pressure reducing valve, relief valves and a discharge pipe. Those are mechanical safety devices, and they can seize, scale up or lose their charge over time. That is why an annual service is a Building Regulations requirement, not a nice-to-have. An engineer checks the vessel charge, exercises the relief valves to make sure they open and reseat properly, and verifies the thermostat and overheat cut-out.
Seeing water drip from a pipe outside your house? On an unvented system that is the relief valve discharging because something upstream has failed, usually the expansion vessel losing its air charge. It is a warning, not a nuisance, and that pipe must never be capped off.
Water gone lukewarm, running out sooner than it used to, or rumbling as it heats? Usually scale on the coil, a failing immersion element, or a thermostat that has drifted.
Give us a ring on 07960 042563 and we will sort it.
Full details at https://manchestergasandheating.co.uk/hot-water-cylinders-explained-vented-unvented-and-what-yours-needs/
